try to use timer interrupt

main.c

@@ -1,42 +1,56 @@
 /**
  * @file main.c
- * @brief Bike rear light implementation for ATTINY202.
- *
+ * @brief Bike rear light implementation for ATTINY202 with low-power standby.
  */
 
 #include <stdint.h>
 #include <stdbool.h>
 #include <avr/io.h>
 #include <util/delay.h>
+#include <avr/sleep.h>
+#include <avr/interrupt.h>
 
-#define BUTTON_PIN_MASK 0x01 // PA0 TODO: using RESET/UPDI pin
-#define PA1_SET_MASK 0x02    ///< LED 1–2
-#define PA2_SET_MASK 0x04    ///< LED 3–6
-#define PA3_SET_MASK 0x08    ///< LED 7–8
-#define PA6_SET_MASK 0x40    ///< Green LED pin
-#define PA7_SET_MASK 0x80    ///< Red LED
+#define BUTTON_PIN_MASK 0x01 // PA0
+#define PA1_SET_MASK 0x02    // LED 1–2
+#define PA2_SET_MASK 0x04    // LED 3–6
+#define PA3_SET_MASK 0x08    // LED 7–8
+#define PA6_SET_MASK 0x40    // Green LED
+#define PA7_SET_MASK 0x80    // Red LED
 
-#define MAIN_LOOP_SLEEP 10U                 // Main loop delay in ms
+#define MAIN_LOOP_SLEEP 50U                 // Loop period in ms
 #define BUTTON_LONG_PRESS_DURATION_MS 1000U // Long press threshold
-#define BUTTON_IGNORE_DURATION_MS 1000U     // Time button ignored after long press
+#define BUTTON_IGNORE_DURATION_MS 1000U     // Ignore after long press
 
-/** Convert milliseconds to system ticks */
 #define MS_TO_TICKS(ms) ((ms) / MAIN_LOOP_SLEEP)
 
-/** Global flags */
-volatile bool bLedEnabled = true;
+volatile bool bLedEnabled = false;
 volatile bool bBtnPressed = false;
 
-// Forward declarations
-void blinkLed(bool resetCounters);
 static inline void leds_off(void);
 static inline void leds_on(void);
 static void battery_level_indicator(void);
 static void handleSwitch(void);
+void blinkLed(bool resetCounters);
 
-/**
- * @brief Main entry point
- */
+/* --- Timer init: Use RTC PIT for periodic wake-up --- */
+void init_timer(void)
+{
+    RTC.CLKSEL = RTC_CLKSEL_INT1K_gc; // 1 kHz ULP clock for RTC
+    while (RTC.STATUS > 0)
+    {
+    } // Wait for sync
+
+    RTC.PITINTCTRL = RTC_PI_bm;        // Enable PIT interrupt
+    RTC.PITCTRLA = RTC_PERIOD_CYC64_gc // ≈64 ms wake-up (~50 ms)
+                   | RTC_PITEN_bm;     // Enable PIT
+}
+
+ISR(RTC_PIT_vect)
+{
+    RTC.PITINTFLAGS = RTC_PI_bm; // Clear interrupt flag
+}
+
+/* --- MAIN --- */
 int main(void)
 {
     // Configure LED pins as outputs
@@ -52,7 +66,13 @@ int main(void)
 
     bool bLedEnabledOld = bLedEnabled;
 
-    while (true)
+    cli();
+    init_timer();
+    sei();
+
+    set_sleep_mode(SLEEP_MODE_STANDBY);
+
+    while (1)
     {
         handleSwitch(); // Check switch state
 
@@ -88,7 +108,9 @@ int main(void)
             }
         }
 
-        _delay_ms(MAIN_LOOP_SLEEP);
+        sleep_enable();
+        sleep_cpu(); // Sleep until PIT wakes
+        sleep_disable();
     }
 }
 
@@ -279,7 +301,7 @@ void blinkLed(bool resetCounters)
         if (counter >= T250)
         {
             counter = 0;
-            state = 0; // restart normal sequence
+            state = 0;
         }
         break;
     }